1. Field of the Invention
The present invention relates to an array antenna and antenna system, and more particularly, to an array antenna and antenna system achieving a comparable detecting range in a horizontal direction and a vertical direction.
2. Description of the Prior Art
An array antenna is an antenna system composed of a plurality of identical antennas arranged in accordance with a specific rule. Through proper arrangement of antenna element of the array antenna, a specific radiation pattern is achieved to concentrate a main beam at a specific direction to transmit signals. For example, for vehicular radar systems, the array antenna is configured to perform 2-dimensional sensing in horizontal direction. However, in practical applications, the 2-dimensional sensing over only the horizontal direction may receive reflections from objects (such as notice boards, traffic lights, bridges, buildings, etc.) which are higher than a horizontal plane. Due to hardware limitations, a false alarm is usually caused and system performance is degraded. In such a situation, if the vehicular radar system provides a radio frequency (RF) system with a three dimensional scanning function to sense over both the horizontal direction and the vertical direction simultaneously. Reflections from the horizontal direction and the vertical direction are more distinguishable, such that system reliability is enhanced and the false alarm rate is further reduced.
Traditionally, an intuitive way to obtain sensing capability in different directions is to deploy another set of array antennas, and arrange the array antennas so as to sense over the vertical direction. However, vehicular radar systems utilize wireless signal transceivers disposed inside vehicle bumpers or grills for ranging and information exchange applications. Since shock-absorbing Styrofoam or glass fibers are usually disposed inside the vehicle bumpers, the available space is limited. It is hard to accommodate another set of array antennas. Furthermore, if the vehicular radar systems are produced for sales of after-market, i.e. vendors for the radar systems do not participate in decision-making of materials and thickness of the bumpers, in such a condition, design requirements for the array antenna gain, the area and the radiation patterns become stricter for adapting to different cars.
A dual polarized antenna system including a horizontally polarized antenna and a vertically polarized antenna has been developed in the prior art, to provide object scanning and detecting in both the horizontal direction and the vertical direction. However, it is difficult to achieve the same detection range using the horizontally polarized antenna and the vertically polarized antenna in the prior art, which lowers performance of the antenna system. In addition, the horizontally polarized antenna and the vertically polarized antenna have to be designed individually, and have to be realized by a particular stacking structure, which have high design complexity and production cost.
Therefore, how to achieve substantially same detecting range in the horizontal direction and the vertical direction is a significant objective in the field.